Investigating the Behaviour of Leaky Barriers with Flume Experiments and 3D Modelling

Abstract

Leaky barriers are small flood defences, inspired by the beaver dams and large woody debris found in watercourses. They are installed to slow down flows, encourage water onto the floodplain, and increase channel roughness. While one barrier on its own will not have much of an effect, the combined effect of many barriers across a channel network could attenuate flood peaks. However, as it is difficult to measure the impact of leaky barriers on flood events in the field, their behaviour is still largely unquantified. A fluid dynamics approach, pairing hydraulic flume experiments with 3D modelling, could address this evidence gap. Here, we used 0.3 m- and 1 m-wide flumes to measure the impact of a simple horizontal barrier under different flow rates and channel slopes. Four of these steady-state experiments were recreated with the volume of fluid solver interFoam, part of the OpenFOAM library. First, hybrid meshes were created using Ansys software. Tetrahedral cells capture the shape of the barrier, but more efficient hexahedral cells fill the rest of the domain, with both zones having inflation layers along walls. These meshes were then imported into OpenFOAM for use with interFoam. Local time-stepping and first-order spatial discretisation took the simulations quickly to a steady state. Finally, these initial results were used to start off a time-accurate simulation with second-order spatial discretisation. The results show that interFoam is acceptable for simulating such steady-state cases.